My understanding is that it's a couple of weeks for neurologic adaptation (i.e. you get better at doing stuff without actually getting more muscle) and ~6 for genuine muscle growth. I don't know how this corresponds to cardio exactly but some of it must carry over; at least the consumption of whatever muscles you are using and the heart itself. Lungs may be some black magic, I could not have less of an idea.
My understanding is that it's a couple of weeks for neurologic adaptation (i.e. you get better at doing stuff without actually getting more muscle) and ~6 for genuine muscle growth. I don't know how this corresponds to cardio exactly but some of it must carry over; at least the consumption of whatever muscles you are using and the heart itself. Lungs may be some black magic, I could not have less of an idea.